The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
Lubricious coatings are designed to provide medical devices with a slippery surface, which enhances the comfort of a subject during insertion, placement and/or removal of the medical device. This is because a lubricious coating reduces the insertion force and allows the medical device to traverse the tissue/body lumen it is inserted into more easily. Such coatings also avoid severe abrasion between the surface of the device and the tissues/body lumen of the subject. Typical medical devices that are coated with a lubricious coating include guidewires, catheters and other medical devices that are required to be inserted into a subject (and potentially removed thereafter).
In general, such lubricious coatings may contain a single layer or two layers—a top layer and a bottom layer. The top layer generally contains a hydrophilic polymer and is intended to come into direct contact with the tissues and/or body lumen of a subject. The bottom layer is intended to provide improved adhesion between the top layer and the surface of the medical device. The majority of effort in this field has focused on providing improved top layers/single layer formulations, as this is what comes into direct contact with the subject. International patent application publication Nos. WO 2007/065722, and WO 2008/104573 disclose the use of a polyelectrolyte material as part of a layer intended to be in direct contact with a lumen of a subject. International patent application publication No. WO 2011/157805 discloses the use of a Norrish type II photoinitiator comprising substituted benzophenone, xanthone, tioxanthone or anthraquinone as part of a similar layer.
International patent application publication No. WO 2008/104572 discloses the use of a supporting polymer backbone with reactive moieties that can capture a hydrophilic polymer coating layer. The problem with this design is that when the coated medical devices are inserted into human body, the entrapped hydrophilic polymer layer has a tendency to rub off due to abrasion, resulting in a high level of particulate/migrable matter in the lumen of the subject, which is undesirable. Hence, one of the main challenges being faced by the industry is to reduce the release of particulate/migrateable matter from lubricious coatings on a medical device following insertion into a subject. The particulates formed from the polymer/coating material may be dangerous to human body in some application, such as angioplasty and stent placement, due to their ability to migrate and, in some cases, aggregate.
While the top (i.e. functional) layer provides lubricity, the base layer of a two layer coating is intended to ensure the stability of the coating. However, there is a broad range of materials used in medical devices that need to be coated to ensure hydrophilic lubricious performance of the device. These medical device materials include, but are not limited to, metals, polyurethane (PU), polyvinyl chloride (PVC), latex, pebax, nylon, polypropylene, polyethylene (HDPE and LDPE), fluorinated ethylene propylene (FEP), poly(ethene-co-tetrafluoroethene) (ETFE), poly(ethylene terephthalate) (PET) and silicone elastomers etc, all of which are potential substrates for a lubricious coating. Some of these materials are very hydrophobic (low surface energy), such as PP (polypropylene), HDPE, FEP and ETFE. To achieve a stable hydrophilic coating on these very hydrophobic materials remains challenging. International patent application publication Nos. WO 2011/157805 and WO 2008/031596 only use PVC and PU as the substrate materials, and none of the exemplified coatings have sufficient adhesion to substrates such as silicone, PP, FEP and the like. Further, the exemplified coatings on such materials have poor adherence and durability and are relatively easy to rub off from the substrate surface when the entire device (including coating) has been wetted. It is possible to improve the adhesion of a hydrophobic substrate and a hydrophilic coating layer using pretreatments, such as solvents, plasma and harsh chemical solutions. These pretreatments attempt to reduce the surface free energy of the substrate, so that a hydrophilic coating solution can spontaneously spread on it. However, the use of pretreatments increases the manufacturing cost and reduces the efficiency of manufacturing.
Therefore, there remains a need to: (1) develop a coating with negligible release of particulates/migrateables from the top coat of a two-layer coating; and (2) develop a versatile base coat platform to be directly applied on different substrates to achieve robust adhesion between substrate and lubricous functional layer. It is possible that solving (2) may result in the improvement of (1).